1. Field of the Invention
The present invention relates to a method of fabricating masks for extreme ultra-violet and deep ultra-violet lithography using structures of etch-resistant metal/semiconductor compound formed by a direct-write electron beam lithography process.
2. Brief Description of the Prior Art
The fabrication of very large scale integrated circuits combined with the miniaturization of electronic devices requires several improvements of the lithography techniques that are already used for industrial production. Deep ultra-violet (DUV) lithography is the technique used in large scale production of devices and circuits, using light sources with 248, 193 and 157 nm wavelengths [J. Canning (1997), J. Vac. Sci. Technol., B15, 2109]. The fabrication of devices with a resolution of the order of these wavelengths is limited by these wavelengths. To solve these problems, several approaches are evaluated. One of these approaches is to introduce correction patterns in the exposed mask patterns in order to compensate for the deformation induced by the UV limitations at these wavelengths [S. R. J. Brueck, Xiaolan Chen, (1999), J. Vac. Sci. Technol., B17, 908]. These corrections patterns, often referred to as optical proximity correction (OPC), and the fabrication of masks for high resolution purposes (with or without proximity corrections) requires the use of a high resolution electron beam lithography technique. Current techniques use polymeric or organic resist as the electron sensitive material, which are often limited in achievable resolution and have a poor resistance to chemical etching used afterward to transfer the pattern from the exposed resist to the mask itself. Also, polymeric or organic resists must be spin-coated, a process that causes undesirable particles to be included in the resist layer. These particles in turn cause defects in the exposed patterns, which are detrimental to the process.
Another approach is to reduce the wavelength of the emitted UV light. This approach requires reflective optical elements for wavelengths of the order of 10 nm (Extreme Ultra-Violet or EUV) [C. W. Gwyn, R. Stulen, D. Sweeney, D. Attwood, (1998), J. Vac. Sci. Technol., B16, 3142]. One element is the reflective mask, which is made of absorbent regions on a reflective multi-layer system [P. J. S. Mangat et al. (1999), The 43rd International Conference on Electron, Ion and Photon Beam Technology and Nanofabrication, Abstracts of conference, 456]. The resolution required in the fabrication of these masks is less important since no optical proximity correction is needed at these wavelengths. However, the absorbent layer must be thick enough for it to absorb over 90% of EUV light. This requires metallic layers with a thickness of the order of 100 nm. In the patterning process for these structures, electron-beam lithography is often used. However, the poor resistance of electron-sensitive resists implies the use of thick resist layers which reduces the achievable resolution. Also, the problems caused by the spin-coating of polymeric or organic resists are also a concern in the fabrication of masks for EUV lithography.
In 1997 and 1998, a resistless sub-micron lithography technique using the electron beam energy to form silicide was discovered [U.S. Pat. No. 5,918,143 granted to Beauvais et al. for xe2x80x9cFabrication of sub-micron silicide structures on silicon using resistless electron beam lithographyxe2x80x9d ] and its application to the fabrication of masks for X-ray lithography and nano-imprint lithography were demonstrated. This technique eliminates the need for polymeric or organic resists and solves several problems associated with electron beam lithography.
An object of the present invention is to use electron beam lithography for the fabrication of masks for DUV and EUV lithography, thus eliminating several problems associated with polymer or organic resist based processes.
More specifically, the present invention is concerned with a method for fabricating a mask for deep ultra-violet lithography, comprising providing a substrate made of material transparent to deep ultra-violet radiation, depositing on the substrate a layer made of material opaque to deep ultra-violet radiation, depositing on the layer of opaque material two superposed layers including a layer of semiconductor material and a layer of metal capable of reacting with the semiconductor material to form an etch-resistant metal/semiconductor compound, producing a focused electron beam, applying the focused electron beam to the superposed layers of metal and semiconductor material to cause diffusion of metal and semiconductor material in each other and form etch-resistant metal/semiconductor compound, displacing the focused electron beam on the superposed layers of metal and semiconductor material to form a structure of etch-resistant metal/semiconductor compound, and etching the layer of metal, the layer of semiconductor material and the layer of material opaque to deep ultra-violet radiation to leave on the substrate the structure of etch-resistant metal/semiconductor compound and the layer of opaque material underneath that structure to thereby form the mask for deep ultra-violet lithography.
Preferably, the transparent material of the substrate is selected from the group consisting of quartz and glass, the material opaque to deep ultra-violet radiation comprises chromium, the metal is selected from the group consisting of nickel, chromium, copper, palladium and platinum, and the semiconductor material comprises silicon.
The present invention further relates to a method for fabricating a mask for extreme ultra-violet lithography in which a substrate made of extreme ultra-violet reflective material is provided. An extreme ultra-violet absorbent layer is deposited on the substrate. For depositing this extreme ultra-violet absorbent layer, an etch stop sub-layer is deposited on the substrate, a repair buffer sub-layer is deposited on the etch stop sub-layer, and a sub-layer made of extreme ultra-violet radiation absorbent material is deposited on the repair buffer sub-layer. Two superposed layers are then deposited on the extreme ultra-violet absorbent layer, these two superposed layers comprising a layer of semiconductor material and a layer of metal capable of reacting with the semiconductor material to form an etch-resistant metal/semiconductor compound. A focused electron beam is produced and applied to the superposed layers of metal and semiconductor material to cause diffusion of metal and semiconductor material in each other and form etch-resistant metal/semiconductor compound. The focused electron beam is displaced on the superposed layers of metal and semiconductor material to form a structure of etch-resistant metal/semiconductor compound. The method finally comprises etching the layer of metal, the layer of semiconductor material, the sub-layer made of extreme ultra-violet absorbent material, and the repair buffer sub-layer to leave on the substrate (a) the structure of etch-resistant metal/semiconductor compound and (b) the sub-layer made of extreme ultra-violet absorbent material and the repair buffer sub-layer underneath this structure to thereby form the mask for extreme ultra-violet lithography.
Advantageously, the extreme ultra-violet reflective material of the substrate comprises very thin layers of molybdenum in between very thin layers of silicon, the etch stop sub-layer is made of chromium, the repair buffer sub-layer is made of a material selected from the group consisting of SiO2 and SION, the extreme ultra-violet radiation absorbent material is selected from the group consisting of Ta, W, Cr and TaSi, the semiconductor material comprises silicon, and the metal is selected from the group consisting of nickel, chromium, copper, palladium and platinum.
The objects, advantages and other features of the present invention will become more apparent upon reading of the following non restrictive description of preferred embodiments thereof, given for the purpose of exemplification only with reference to the accompanying drawings.